A study on effect of melt fraction relaxation factor in numerical simulation with the enthalpy-porosity method for latent heat storage

• The influence of relaxation factor in enthalpy porosity approach is studied for Latent Heat Storage devices. • Insightful melt fraction evolution trends are presented. • The relationship between melt fraction and temperature rise is established, for varying relaxation factors. • The influence on natural convection jump is quantified. Among many approaches adopted for simulating the latent heat based phase change devices, the enthalpy-porosity method is the most accepted among the researchers. Also, the melt fraction based under relaxation factor significantly influences the progression of the melting simulations. No prior studies are available in this regard. So, for the enthalpy-porosity method, to understand the influence of the relaxation factor, it is varied in the range of 0.1 to 1.0. The present investigation focuses on prominent aspects of Phase Change Material (PCM) melting, including total melting time, melt fraction evolution, natural convection jump, and the average temperature of the PCM. It is found that the total melting time exhibits an exponential variation with relaxation factors (RF), showing minor variations within the region of 0.5 < RF ≤ 1.0 and substantial changes within 0.1 ≤ RF ≤ 0.5. The fourth quarter exhibits the longest melt duration, equivalent to the cumulative duration of the first three quarters. Lower RFs have shown early peaking of temperature during the initial stages, causing prolonged melting, while RFs >0.5 have minimal temperature shifts. The magnitude of natural convection jump is found to have minimal effect due to the change in the relaxation factor.